This invention relates to the art of bottle closures, and more particularly to a compression failure resistant tamper evident bottle cap.
Nowadays, many bottle caps have a band which tears away from the rest of the cap, remaining with the bottle neck, when the cap is removed for the first time. One can visually, or by feel, detect when such a cap has been removed and then reinstalled, because of the failure of the anti-tamper feature. Such caps, once made of metal, now are usually molded from a plastic polymer.
The tamper-evident band is normally smaller in diameter than a retaining flange on the bottle finish, and is pushed over the retaining flange at the factory when the cap is installed. The band is connected to the rest of the cap along a weakened peripheral line, for example define by a series of perforations which weaken the material and provide a locus for failure when the cap is removed.
A problem with some caps of this type is that during installation, as the band is being forced over the bottle's retaining flange, the resistance force not only puts large axial compression forces on the weakened peripheral line: it also expands the band radially. The combination of these two factors gives rise to the possibility that the band will tend to ride up over (around) the bottom of the cap, failing the tamper-evident features-prematurely.
EP228618A2 discloses a tamper-indicating closure comprising means for preventing undue diametral expansion of the tamper-evident band. The tamper-evident band is provided with inwardly and upwardly directed protrusions on its upper edge. During relative axial movement between the tamper-evident band and the skirt of the closure, these projections engage the bottom edge of the skirt of the closure. The protrusions comprise an inclined upper and outer surface. When this surface engages the lower edge of the skirt, the tamper-evident band is prevented from unduly expanding. Such means, however, need a separate cutting operation for their fabrication and work only if there is a relative axial movement between the tamper-evident band and the skirt of the closure. This axial movement may lead to premature failure of frangible bridges connecting the tamper-evident band to the skirt.